One example of conventional pump apparatuses will be explained in reference to FIG. 6. As shown in FIG. 6, a pump apparatus 1 includes a uniaxial eccentric screw pump 2 and a rotor drive mechanism 4 configured to rotate a rotor 3 provided in the uniaxial eccentric screw pump 2. The uniaxial eccentric screw pump 2 is configured such that the external screw type rotor 3 is fittingly inserted in an internal screw type inner hole 5a of a stator 5. By rotating the rotor 3 in a predetermined direction, a transfer fluid, such as a liquid, can be suctioned from a suction port 6 for example, held in a space between the rotor 3 and the stator 5, transferred, and then discharged from a discharge port 7. At this time, the rotor 3 carries out an eccentric rotational movement, i.e., rotates while carrying out a revolution movement about a central axis 8 of the stator inner hole 5a shown in FIG. 6. The rotor drive mechanism 4 realizes the eccentric rotational movement of the rotor 3.
The rotor drive mechanism 4 shown in FIG. 6 includes a driving shaft 9 rotated by a rotary driving portion (for example, an electric motor) 11 and a connecting shaft 10 connected to a tip end portion of the driving shaft 9. A tip end portion of the connecting shaft 10 is connected to a rear end portion (base end portion) of the rotor 3.
To be specific, when a rotating shaft 11a of the rotary driving portion 11 rotates, this rotation is transferred through a coupling 18, the driving shaft 9, and the connecting shaft 10 to the rotor 3, and thus, the rotor 3 carries out the eccentric rotational movement. With this, the transfer fluid can be suctioned from the suction port 6 and discharged from the discharge port 7.
As shown in FIG. 6, the tip end portion of the connecting shaft 10 and the rear end portion of the rotor 3 are connected to each other via a first joint portion (universal joint) 12, and the tip end portion of the driving shaft 9 and a rear end portion of the connecting shaft 10 are connected to each other via a second joint portion (universal joint) 13. The first and second joint portions 12 and 13 and the connecting shaft 10 are covered with a joint cover 14 made of, for example, synthetic rubber. The joint cover 14 prevents the transfer fluid, suctioned from the suction port 6 to a fluid accommodating space 16 of a casing 15, from contacting the first and second joint portions 12 and 13 and the connecting shaft 10.
Another example of the pump apparatus 1 is disclosed in PTL 1.